package dome2;

import java.util.Arrays;

public class PriorityQueue {
    public int[] elem;
    public int usedSize;

    public PriorityQueue() {
        elem = new int[10];
    }

    /**
     * 建堆的时间复杂度：
     *
     * @param array
     */
    public void createHeap(int[] array) {
        for (int i = 0; i < array.length; i++) {
            elem[i] = array[i];
            usedSize++;
        }
        for (int parent = (usedSize - 1 - 1) / 2; parent >= 0; parent--) {
            shiftDown(parent, usedSize);
        }
    }

    /**
     * @param root 是每棵子树的根节点的下标
     * @param len  是每棵子树调整结束的结束条件
     *             向下调整的时间复杂度：O(logn)
     */
    private void shiftDown(int root, int len) {
        int child = root * 2 + 1;
        while (child < len) {
            if (child + 1 < len && elem[child] < elem[child + 1]) child++;
            if (elem[child] > elem[root]) {
                swap(elem, child, root);
                root = child;
                child = root * 2 + 1;
            } else {
                break;
            }
        }
    }

    private void swap(int[] elem, int child, int root) {
        int cur = elem[child];
        elem[child] = elem[root];
        elem[root] = cur;
    }


    /**
     * 入队：仍然要保持是大根堆
     *
     * @param val
     */
    public void push(int val) {
        if (isFull()) Arrays.copyOf(elem, elem.length * 2);
        elem[usedSize] = val;
        shiftUp(usedSize);
        usedSize++;

    }

    private void shiftUp(int child) {
        int root = (child - 1) / 2;
        while (root >= 0) {
            if (elem[root] < elem[child]) {
                swap(elem, root, child);
                child = root;
                root = (child - 1) / 2;
            } else {
                break;
            }
        }
    }

    public boolean isFull() {
        return usedSize == elem.length;
    }

    /**
     * 出队【删除】：每次删除的都是优先级高的元素
     * 仍然要保持是大根堆
     */
    public void pollHeap() {
        if(isEmpty()) return;
        swap(elem,0,usedSize);
        usedSize--;
        shiftDown(0,usedSize);
    }

    public boolean isEmpty() {
        return usedSize == 0;
    }

    /**
     * 获取堆顶元素
     *
     * @return
     */
    public int peekHeap() {
        return elem[0];
    }
}